Various energy management schemes have been proposed which require that utility customers limit their electrical power consumption during periods of peak demands or as a means of reducing overall utility costs. In such schemes, the maximum load which each customer is allowed to place on the utility has been somewhat arbitrarily limited. Representative of such approaches is that disclosed in U.S. Pat. No. 4,247,786 to W. P. Hedges in which each user or consumer selects the maximum load irrespective of actual usage of power. Although the foregoing and other approaches are effective in reducing the customer's overall utility costs, they present a number of problems both to the customer and to the utility. The arbitrary selection of the demand limit is usually based on worst case conditions so that, for example, the demand limit must be selected such that the user does not suffer undue discomfort on the colder days of the year; however, at other times of the year the user would then save less and the utility would have less reduction as a result of the higher demand. Thus, if a peak usage period occurred in the summer months when there was no heating load, no reduction in demand could be effected by the system because of the high demand level selected.
Among other problems associated with conventional demand reduction schemes is that the utility only knows how much energy is used by a customer but not the rate of use or the demand of the customer. As such, neither the utility nor the customer has accurate guidance with respect to proper setpoint selection or utility control. Further, utilities are in the business of selling energy; however, imposing arbitrary demand limits can only reduce the amount of energy sold during periods when demand control is not required. Still further, arbitrary and customer selectable demand control setpoints must be verified by installation of expensive meters which record the demand usage and which periodically must be read, reset and billed.
Accordingly, it is desirable to provide an energy managment method and system which will enable the utility to modify the rate of using energy at any time of the year in accordance with actual demand usage patterns of each user during that period, will allow variable demand control limit selection which will thoroughly and equitably distribute the reduction among its customers and will allow the utility to maximize its energy sales. At the same time it is desirable to avoid the need for demand meters, to efficiently reduce the total load of the utilities generating facilities as well as to proportionately reduce the amount of energy consumed in accordance with the actual usage patterns of each user.